AVR 250 sub crossover problem

Guest

I recently purchased an AVR 250 and am wondering about its internal sub crossover settings. I've been running the bass management frequency sweep (20 hz - 150 hz) on the Digital Video Essentials DVD targetted directly at the subwoofer channel. My sub is passive and has no variable crossover setting. According to the bass management sweep, it rolls off around 145 hz. But no matter what setting I choose for the sub crossover within the AVR 250, my sub continues to roll off at exactly the same point in the sweep. Does this mean that the crossover function in the 250 is not working? If I set the crossover to 60 hz, shouldn't that mean that I hear little or nothing beyond the 60 hz point in the sweep? Or is there something else I should be aware of?

Active Member

If your sub is passive how are you running it. The AVR250 does not have a power amplfier for the sub. If you have attached it to one of the other channels then that ouptut will not have been filtered by the crossover. Only the line level ouput on the Sub phono/RCA connector has the filtered sub ouput on it. To use this output you will need an external power amplifer for a passive sub.

Active Member

I think I have worked out what is going on. Your disc has the sweep recorded on the LFE channel. In the dolby spec is assumed that the LFE channel has been recorded for playback on a subwoofer and so it is already band limited, so the LFE itself does not get filtered. The LFE channel is only used for bass effects in films, it is not used for music.

To see the effect of the Xover setting you would need to input the sweep onto E.g front left and have left and right set for small speakers. Then the xover would redirect the appropriate part of the signal to the subwoofer.

Guest

You're probably right about the dedicated LFE info, so I tried adjusting the crossover and listening to the results on the left channel alone. There still doesn't seem to be any appreciable difference between crossover settings, so I'm not sure what's up. I've played with the internal crossovers on a couple active subs since my last post and have noticed that there is very little difference between 40 hz and 160 hz settings, so perhaps it's simply a matter of my lack of knowledge about the gentleness of the rolloff usually employed on crossover circuits. I expected a brick wall at whatever point I would set the crossover, and that's clearly not how they're designed.

So, can you tell me just how gentle the rolloff on the AVR 250 crossover is in technical terms? Maybe that'll help.

Of course, another possibility is that the crossover only applies to stereo material, since the adjustment meter is sandwiched between the "stereo mode" and "stereo sub volume" settings. I've only done my testing in digital surround mode. Is it possible that the crossover doesn't apply to surround material because of the LFE track?

Active Member

The crossover definately applys to digital as well as processed analogue sources, it is a dolby and DTS requirement for certification.

The crossover filters are second order which means they roll of at 12dB per octave. I have to admit I have never listened to just the effect of moving the crossover so can't comment on how it would sound.